The incorporation of flavorants in tobacco products is an important development in the tobacco industry due to the lowered aromaticity of the available tobacco and to the increased preference of some smokers for filter cigarettes. The addition of certain desirable flavorants to tobacco is limited by their volatility which causes them to be lost or diminished in quantity during processing and storage of the tobacco product. This problem is even more acute for filter cigarettes containing active adsorbent, such as charcoal, in the filters. During the processing and storage of this type of product, volatile flavorants migrate from the tobacco and are irreversibly bound by the active adsorbent, thereby depleting the flavorant in the product and possibly altering the effectiveness of the active adsorbent in its selective removal of undesirable smoke components.
Menthol is a flavorant which has received high acceptance as an additive to tobacco products because of the pleasant cooling effect and desirable aroma and flavor characteristics which it imparts to the smoke. Its high degree of volatility and ease of sublimation have presented problems in the manufacturing operations and, in addition, have resulted in a decreased shelf-life of the product due to losses of menthol by diffusion on storage.
In an attempt to alleviate these problems, it has been suggested that menthol might be adsorbed on a suitable support, such as activated charcoal or fuller's earth, and that the resultant composition might then be added to the tobacco. Attempts to pursue this method have not been satisfactory. The menthol yields from such adsorbents have been found to be very low. Moreover, this method obviously necessitates incorporation of the adsorbent into the tobacco, and such a foreign material can result in an undesirable appearance as well as give rise to uneven burning of the tobacco.
In order to overcome these difficulties, menthol has been incorporated into the tobacco as a part of a compound (i.e., a menthol-release agent) in such form that upon burning of the tobacco, the compound is decomposed to yield the desired menthol flavorant. While considerably more satisfactory than earlier attempts, even this technique has evidenced certain drawbacks.
Bavley et al., U.S. Pat. No. 3,312,226, describes a processs whereby menthol is incorporated into tobacco as the carbonate ester of various alcohols, particularly one such as linalool, which are themselves useful flavorants. Upon pyrolysis of these carbonate esters, incident to the normal burning temperatures of the tobacco, the menthol is released to flavor the smoke. However, these simple carbonate esters have not proven wholly satisfactory. They retain one of the difficulties of menthol itself, in that they are somewhat susceptible to migration in the tobacco, and thereby prevent the strict control of quantitative release of menthol to the tobacco smoke during burning. Additionally, the second alcohol of the carbonate ester can prove susceptible to chemical alteration during pyrolysis, thus giving rise to undesirable chemical fragments which can add a chemical aftertaste to the smoke.
The Mold et al. U.S. Pat. Nos. 3,332,428 and 3,419,543, offer a slightly different approach to the problem of adding menthol flavor to a tobacco smoke. These patents, like that of Bavley et al., rely upon the formation of a carbonate ester to bind the menthol in a release agent. Here, however, a polyhydroxy compound such as monosaccharide, disaccharide, trisaccharide, polysaccharide, or glycol is used to fix the menthol in the tobacco. Again there are certain drawbacks.
Because the alcohol linkages of these saccharides and glycols are only primary or secondary in character, the efficiency with which the menthol can be regenerated upon pyrolysis is limited, owing to the opportunity for dehydration of the menthol moiety. Additionally, where attempts were made to utilize menthol-release agents of high menthol proportion (i.e., agents which would release a high proportion of menthol per unit weight) it was discovered that menthenes were often produced in addition to menthol elimination, thereby resulting in a bitter tasting tobacco smoke.
The Rundberg, Jr. et al. U.S. Pat. No. 3,887,603 describes the development of a new type of menthol-release agent for imparting menthol flavor to tobacco smoke with a high efficiency of menthol-release upon pyrolysis under normal smoking conditions. The menthol-release agent is a polymeric .lambda.-menthyl carbonate ester composition characterized by the presence of a tertiary alcohol ester attachment. Although the said tertiary alcohol moiety renders deesterification as a preferred decomposition mechanism under smoking conditions, there has remained a need for improved menthol-release agents which are conveniently synthesized from readily available starting materials, and which exhibit increased menthol-release efficiency without being deleterious to the flavor of the resultant tobacco smoke.
Accordingly, it is a main object of this invention to provide an improved type of menthol-release agent which is characterized by a substantial lack of mobility and/or volatility at ambient temperatures when incorporated in a tobacco composition.
It is another object of this invention to provide a unique polymeric composition which is adapted to release menthol to tobacco smoke under normal smoking conditions with optimal efficiency and with non-deleterious effect on the flavor of the resultant tobacco smoke.
It is a further object of this invention to provide a novel class of .alpha.-substituted-vinyl menthyl carbonate esters, and a method for their preparation from readily available starting material.
Other objects and advantages of the present invention shall become apparent from the following description and examples.